The age-old question of, “Why is that tree looking so sickly?” is one that is at the crux of integrated pest management, plant health care, diagnosis, monitoring and scouting. Another way to describe this time-honored query is more along the lines of what most customers think, which is, “What’s wrong and how do we fix it?” In a landscape with healthy soil, abundant light and appropriate rainfall, problems tend to be few and far between. Sure, living organisms can cause injury; we see it every day. But arborists would be doing their clients a huge disservice if insects and diseases were the only influencers that were considered as causes. Nonliving, or abiotic factors, must be considered as well.
Eyes wide open
Experienced tree service providers know that the list of possible causes of a particular perceived illness is usually long and sometimes uncertain. It helps to add clarity by working through a step-by-step process that contains several components:
- Identification of the tree species — the starting point for all problem causes.
- Gathering of relevant historical information about the site and surroundings, both in recent times and over the past five to seven years. This could include utility line trenching, soil moved for construction, cold winters, hot summers, neighbor’s pool parties, lawn service applications, etc.
- Consideration of the three basic categories of causal agents: (generally) diseases, insects and nonliving influences.
- Review of previous maladies of/on the tree: what the tree has been treated for by your company or other companies.
- Matching the general appearance of the tree with the general symptoms of previous tree problems: spots on leaves, holes in trunk, thin crown.
- Investigating known influences of the tree in question by species, such as spruce and spruce spider mites or poplar and cytospora canker; comparing the appearance of the leaves, bark or branches to the photos of documented resource guides.
- Gaining outside information and assistance from university extension personnel and fellow arborists.
When the above series of steps is utilized, the list of possibilities usually shrinks from many to few. A sometimes known, sometimes unknown “X-factor,” or little-known secret, is that well over half of the primary causes of tree decline or symptom expression are due to nonliving or abiotic influences.
Diagnosing tree problems can be difficult, especially in one-off situations, such as when a new customer calls out of the blue and asks for the diagnosis of a sick-looking tree, and the only information provided is that, “it just started looking that way last week.” Such a scenario usually brings the internal response from veteran arborists, “Oh, yeah, and if that’s true, pigs should be flying right about now.”
Instead of looking at a tree for the first time, it’s much easier to find success with causal determination if a scouting and monitoring protocol has been in place. Scouting, sometimes referred to as inspection, is usually a one-time endeavor. It’s used for both investigation of a poor-looking tree or proactively in an effort to investigate the entire property, much like an air conditioner inspection at the beginning of summer or an annual doctor visit to detect early signs of heart disease.
While these types of inspection are helpful, it’s wise to go one step further, to scout on a regular basis through the season – to monitor. Weekly, biweekly, monthly or seasonal scouting pays big dividends through being able to spot a disease, insect or abiotic causal agent. Spending time in a landscape gives the inspector an important feel for the issues at hand and the changes that are occurring over time. As well, it’s a great bottom line profit center for tree service companies, as monitoring is a legitimate arboricultural service that utilizes the technicians’ training, experience and education for the good of the customer.
After each scouting, a quick but pithy report on the trees in the landscape should be generated, noting current age, condition and location of concerns for each species. This type of tree care that involves frequent inspections puts the inspector way ahead of the game, allowing for the gathering of large amounts of information about the site, the neighboring sites, the planting process and other contributing factors.
Common abiotic problems
When a tree fails to express the symptoms of disease, insect, nematode or animal injury, other influencing factors are responsible. Some of the more common ones are:
- Moisture:Each tree species has an ideal moisture level for its root system. Others tolerate a wide variety of soil moisture conditions. When trees experience too little for a long period, it is generally referred to as drought. At the other end of the spectrum, when too much water is received, the spaces between soil particles fill up with excessive water, replacing the oxygen. If this occurs for a long period of time, roots tend to rot, soften and fail to function well. Determining if moisture is a causal agent can be difficult, as the excess or lack is present under the soil surface, out of sight of the tree scout. Using a soil probe, such as a piece of rebar or long screwdriver, can be helpful in taking a snapshot of current moisture conditions. Checking the soil moisture level should be a routine part of each scouting inspection.
- Nutrients: Like moisture levels, it’s possible for the soil to provide too much or too little. Nutrient deficiencies often show up on high or low pH and heavy clay or sandy soils, due to the lack of availability and capacity to retain various elements. A condition known as chlorosis can refer to the lack of iron, manganese or other micronutrients, and express symptoms of yellow and stunted leaves with green veins. Soil testing helps greatly to gain insights into nutrient issues.
- Planting errors: Much has been written about approved practices for planting trees, and for good reason – get it right from the start or limit the health for a lifetime. The most common planting errors are planting a tree too deeply, digging an inadequately-sized hole and the incorporation of compost, sand or topsoil next to the roots. Each of these has consequences; deep planting results in an overabundance of soil over the roots, which limits oxygen and development of the roots below the soil surface and reduces lateral stability. If a problematic tree has a trunk with a lack of taper or root flare for the species, it may have been planted too deeply.
- More planting errors: Planting holes that are too small to accommodate the root system results in a crushing or redirection of roots in a circular fashion. Inexperienced tree planters often dig small holes and force the roots inside or actually cut them off to fit.
When tree roots fail to establish themselves laterally, like the spokes of a bicycle wheel, tree health suffers greatly. Well-meaning individuals often feel that they are doing the tree a favor by modifying the excavated soil with compost or other amendments. While this works well for vegetables or small-rooted plants, when this practice is employed with plants with large woody root systems (trees and shrubs), the result is encircling roots or roots that simply grow to an inadequate length. Stem girdling roots often are visible as a result of planting errors. When they develop, a situation is created where the trunk and roots are expanding in width at the same time and eventually begin to compress the tissues of each, causing stress and constriction on the vascular conductive vessels and reduction in nutrient and water movement.
- Planter boxes/tree surrounds: These devices, used to cover ugly surface roots or simply replace struggling turfgrass with green plants, create conditions where the soil is placed against the tree trunk, keeping it moister than ideal and exclude soil oxygen due to the placement of the soil over the roots. This should be avoided at all costs.
- Physical injury: Tree parts that are physically damaged, either by humans or weather events, are common abiotic influencers. Perhaps the most commonly seen is damage to the lower trunk by lawn maintenance equipment, such as mowers and string trimmers. The removal of bark and exposure of the cambium to the outside elements can be devastating in terms of moisture loss and the creation of openings in the trunk that allow for the development of decay and canker organisms. Mulching practices that begin placement of wood chip mulch 2 inches away from the tree trunk and extend into the landscape as far as the customer will permit go a long way toward preventing these injuries.
- Herbicide injury: Careless applications of weed control products often result in injury to trees, especially ones with foliage within 25 feet of the ground. Wind speed and proximity are usually the main contributors to herbicide injury, where products are applied at speeds above 10 miles per hour and/or where foliage is close enough to the turf to allow for absorption.
- Sunscald: Bark loss on the south, southwest, west and sometimes east side of trunks is often due to sunscald. A common scenario is one where winter sun beats on a tree trunk during the daytime, raising the temperature of the tissue to above freezing; then at night, when the sun sets, the temperature drops to below freezing. When this pattern occurs many nights in a row, the tissue splits, cracks or flakes off, exposing the cambium and sapwood, resulting in drying of inner tissues. Red maples and other thin-barked trees are most susceptible.
- Soil compaction: Compaction, or the compressing together of soil particles, results in less availability for oxygen and water to be present in the root zone of trees. As well, roots already growing at the time of the compaction force are often crushed and damaged. Common causes of compaction are construction equipment and cars/trucks. However, long-term compaction injury can occur from foot traffic and mowing equipment in a chronic fashion over time. Symptoms of compaction include stunted stems with shortened internodes and off-color foliage.
- Temperature injury: Mother Nature can dish out some pretty severe weather at times, causing tree tissues to dry out. While this damage can occur year-round, the periods of most common injury are in spring (as new shoots are being produced), midsummer (especially if soil moisture levels are low) and in the middle of winter (when drying winds cause the stems to lose moisture). When tissues appear brown and lifeless as trees are greening up and/or producing new growth in the spring, consider cold and warm weather injury.